1. Field of the Invention
The present invention relates generally to fusible elements, or fuses of semiconductor device structures, to semiconductor device structures that include fuses, and to methods of fabricating and using the fuses. In particular, the present invention relates to fuses that include metal silicide fuse layers and to methods for fabricating such fuses.
2. Background of Related Art
Computers typically include various types of memory devices. One type of memory device that is typically included in a computer is a read-only memory (“ROM”) device in which data is permanently stored. The programming of a ROM device typically cannot be overwritten or otherwise altered. Thus, ROM devices are useful whenever unalterable data or instructions are desired or required. ROM devices are also nonvolatile devices, meaning that the data stored therein is not destroyed when power to these devices is shut off.
ROM devices are typically designed to execute a specific program and, thus, programmed during fabrication thereof. Typically, the programming of a ROM device is effected by forming permanent electrical connections at selected locations of the memory device, or by “wiring” the memory device in a specific way. As a result, the programming of ROM devices, somewhat undesirably, typically cannot be changed. If a new program is desired, the ROM must be configured or “wired” with the new program.
Another type of memory device that may be used in a computer is the so-called programmable read-only memory (“PROM”) device. Unlike ROM devices, a PROM device may be programmed following fabrication. Some PROM devices are provided with an electrical connection in the form of a fusible link, which is also known in the art to render them programmable as a fuse.
U.S. Pat. Nos. 5,264,725; 4,670,970; 5,661,323; 5,652,175; 5,618,750; 5,578,517; and 3,783,506 disclose exemplary types of fuses that may be used in PROM devices. One type of conventional fuse includes a conductive, metal or polysilicon layer with a narrowed or “necked down” region that forms a conductive link between two wider or otherwise more massive regions of the fuse. This type of fuse may be rendered discontinuous to an electrical current, or “blown” by forcing or driving a relatively high current through the conductive, metal or polysilicon layer. Due to the electrical resistance inherent in the narrowed region, the driving current heats the metal or polysilicon that forms the narrowed region to a temperature above the melting point of the metal or polysilicon, thereby breaking the conductive link of the fuse. Fuses usually blow at the narrowed regions thereof since the current densities and temperatures are highest in that less massive region. Each fuse of a PROM device is thus programmed to one of a pair of conductivity or voltage patterns (i.e., blown or unblown), which corresponds to a bit designated as either a “1” or a “0”, which is the data stored in a particular cell of the memory device associated with the fuse. A PROM device is programmed by selectively blowing fuses along a predetermined sequence, or path.
Fuses may also be used in other types of semiconductor devices, such as static random access memory (“SRAM”) devices and dynamic random access memory (“DRAM”) devices. For example, fuses are useful in SRAM and DRAM devices to select memory circuits that will be used in the finished device (e.g., if a primary circuit is not useful or does not meet quality requirements, that circuit may be deselected and a redundant circuit activated by blowing one or more fuses). The use of fuses in this manner thus improves the fabrication yield of high-density memory devices.
As an alternative to blowing fuses with an electrical current, a laser can be used to blow selected fuses. As memory devices decrease in size and the degree or density of integration increases, the critical dimensions (e.g., fuse pitch) of memory cells become smaller. The availability of lasers suitable to blow fuses is limited since the diameter of the laser beam should not be larger than the fuse pitch. Thus, when lasers are the desired means of programming fuses, the fuse pitch and, therefore, the size of the memory device are dictated by the minimum diameter of laser beams obtainable by current laser technology. Currently, the lower limit of beam diameters for some laser beams is about 5 microns. Using electrical currents instead to blow fuses, therefore, has a greater potential for high-degree integration and decreased size of memory devices. The use of lasers to blow fuses is, therefore, becoming increasingly difficult. Programmable fuses may also be used to address a variety of applications in numerous other types of semiconductor devices.
The metal and polysilicon fuses that are currently used in semiconductor devices are typically “blown” with a laser rather than with an electrical current. The amount of current or laser beam intensity that may be required to “blow” conventional metal or polysilicon fuses may damage regions and structures of the semiconductor device that are proximate to the fuse.
Accordingly, there is a need for semiconductor device fuses that may be programmed, or blown, to impart the fuse with a significantly different conductivity than that of an intact fuse without significantly affecting surrounding structures.